1. Field of the Invention
This invention relates to a method, and an apparatus using the method, for judging a degradation condition of a lead-acid storage battery used for vehicles, and so forth, by using a gas generated at the time of charging the battery.
2. Description of the Related Art
In a solution-type lead-acid storage battery used for vehicles, etc, a degraded condition has been detected, in the past, by measuring the specific gravity of an electrolyte (sulfuric acid). This measurement of the specific gravity is carried out by opening the battery, taking out a small amount of the electrolyte inside the battery and then conducting-the-measurement. Therefore, this measurement cannot be easily carried out in a battery shop or a gas station. The starting performance of a lead-acid storage battery for vehicles has been measured by causing a large current to flow for several seconds and then measuring the 5-second voltage. As this measurement is carried out by using a current exceeding 100 A, it cannot be easily conducted, similar to the measurement of the specific gravity, and the inspection is limited to a specialized garage. Furthermore, the measurement of a battery capacity is carried out by causing a practical battery to discharge at a predetermined current for a predetermined time. Therefore, the testing time is as long as 20 hours or more, inclusive of a charging time, and it takes a long time for an inspector to test the battery.
The method of judging the start performance of the storage battery from the 5-second voltage involves connecting a large clip equipped with a dummy load to a battery terminal. If the large clip is accidentally removed during the discharge for a short time, a spark can develop and may burn a human body. When the test is conducted immediately after the end of charging, a risk of explosion exists if a spark occurs. From the aspect of safety, therefore, the period of the short-time discharge is preferably as short as possible. If the discharge time is extremely short, however, a transient voltage fluctuation of the discharge is affected by an inductance component of a wiring, having no relation with the start performance of the battery and with capacity degradation, and correct measurement cannot be carried out.
Therefore, Japanese Unexamined Patent Publication No. 7-20087 describes a method that involves fitting a hydrogen ion detection element to a lead-acid storage battery to detect the concentration of sulfuric acid as an electrolyte, and always monitors the charge/discharge condition of the lead-acid storage battery. Japanese Unexamined Patent Publication No. 9-33620 describes a method that involves operating a lead-acid storage battery at a constant current for a short time and thus detects the degradation condition of the lead-acid storage battery.
According to the method of Japanese Unexamined Patent Publication No. 7-20087 that detects the concentration of the electrolyte, however, the detection value varies depending on the fitting position of the detection element because the concentration of the electrolyte is not uniform inside the battery or, in other words, because the concentration is high at the upper layer portion and becomes gradually lower towards the lower layer portion. Therefore, the detection value varies depending on the fitting position and this method cannot be said to be an effective degradation condition detection method.
The degradation judgment method for a lead-acid storage battery described in Japanese Unexamined Patent Publication No. 9-33620 involves the steps of connecting a resistor to a lead-acid storage battery through a switch, closing this switch for 200 μsec to 1 msec to discharge the lead-acid storage battery, measuring a difference between a battery voltage at the time of this discharge and a battery voltage under a stable condition after the discharge, calculating a battery capacity or a 5-second voltage from the difference voltage and judging that the battery is degraded when the voltage is below a predetermined value. According to this method, that utilizes a resistor, however, the change of the internal resistance of the lead-acid storage battery is not proportional to the degree of degradation. Namely, when the degree of degradation is small, the change quantity is small and when the degree of degradation becomes large, the change quantity becomes very large, thereby inviting a large detection error.